1. Field of the Invention
This invention relates generally to magnetic storage media, and more particularly to hard disk drive systems that do not provide unique identifying headers on tracks.
2. Description of the Related Art
Conventional hard disk drives typically include one or more magnetic media disks with surfaces divided into concentric tracks for storing data. FIG. 1 shows an exemplary hard disk 100 for storing data in a plurality of tracks 106, 108, 110, 112, 114, and 116. The tracks 106, 108, 110, 112, 114, and 116 may be arranged to define a plurality of data zones. In the hard disk 100, a plurality of servo wedges 104 is spaced about the disk in a spoke-like pattern. The servo wedges 104 subdivide the tracks into a plurality of data frames 102. The portion of a servo wedge 104 within a track is commonly referred to as a servo sector, which separates one data frame in the track from another. Typically, a servo sequencer uses the servo sectors in a track to keep a data head to follow the track and generates end-of-servo (EOS) pulses that mark the ends of servo sectors and the beginnings of data frames. In addition to track following information, a servo sector often contains an ID field that identifies the servo sector and an associated data frame.
In the hard disk 100, data is stored in the data frames, which are typically organized into data sectors, each of which contains the same amount of data such as 512 bytes. The data sectors may include a single data segment that is entirely within a data frame or multiple data segments that are separated from each other by, for example, a servo sector. For constant density recording, the disk area per data byte is constant. However, the amount of data that fits within a data frame varies because the available area depends on the circumferences of the track containing the data frame. Hence, the locations of boundaries of data sectors depend on the track.
When reading or writing a data sector, the boundaries of each data segment need to be identified. One method for identifying data sector boundaries uses information from a header of a data sector to locate splits in the data sector. However, split information stored in headers wastes disk space that could otherwise be used to store data.
Headerless data sectors lack headers containing split information, thereby leaving more disk area for data storage. However, a disk sequencer still requires split information to locate the boundaries of data sectors and segments. A hard disk can store such split information in non-volatile memory, on disk in data sectors, or in a data buffer memory. The split information typically takes the form of look-up tables that describe track formats. For example, a hard disk would typically require one look-up table per zone of tracks having a common track format. Each table contains format words associated with particular data frames, data sectors, or data segments. If, for example, a hard disk having 20 different zones of tracks and 64 embedded servo wedges requires an average of three words of split information per data frame, the hard disk requires 20 look-up tables and a total of 3,840 words of split information.
To avoid degrading performance, a hard disk commonly requires additional data buffer capacity, bandwidth, and processing power for handling the split information. If the required bandwidth is not available when required to transfer split information to a disk sequencer, the hard disk may miss a data sector and delay a transfer for a revolution of the disk. Additionally, firmware executed by a processor in the disk drive must identify the table and split information that corresponds to the current position of the data heads relative to a track being followed. The calculations required to identify the split information can be complex and consume processing power that could otherwise be used for other purposes such as controlling a servo sequencer, managing a data buffer, handling a host interface, and converting read/write requests to a list of physical data sector to be accessed.
Thus, what is needed is a hard drive system that can reduce the amount of split information and reduce the processing demands on a processor in the hard disk drive.
Broadly speaking, the present invention fills these needs by providing a format calculator for headerless hard drive systems for generating sector numbers on track. It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, computer readable media, or a device. Several inventive embodiments of the present invention are described below.
In one embodiment, the present invention provides a headerless hard disk drive system that includes a head-disk assembly, a servo control logic, and a format calculator. The head-disk assembly includes a set of recordable disks for storing data. Each recordable disk having a plurality of tracks with each track having a plurality of servo wedges for dividing the track into a plurality of data frames. In this arrangement, one data frame is associated with one servo wedge and the tracks do not contain any header information that uniquely identifies the data frames in the tracks. The servo control logic coupled to the head-disk assembly to process the servo wedges for generating,a signal that identifies a servo wedge being processed on a track. The format calculator is configured to convert the signal that identifies the servo wedge being processed to an associated sector number on the track. In addition, the format calculator is adapted to compute a set of parameters including ending and beginning split sector sizes and the number of whole sectors in the data frame associated with the servo wedge being processed.
In another embodiment, the present invention provides a hard drive system. The hard drive system includes a head-disk assembly, a servo control logic, and a format calculator. The head-disk assembly includes a set of hard disks for storing data with each hard disk having a plurality of tracks. Each track has a plurality of servo wedges for dividing the track into a plurality of data frames with one data frame being associated with one servo wedge. The tracks in the hard disks do not contain any header information that uniquely identifies the data frames in the tracks. The servo control logic is coupled to the head-disk assembly to process the servo wedges for generating a signal that identifies a servo wedge being processed in a track. The format calculator is adapted to convert the servo wedge identifying signal to an associated sector number that corresponds to the servo wedge being processed in the track. The format calculator is further adapted to compute a set of parameters including ending and beginning split sector sizes and the number of whole sectors in the data frame associated with the servo wedge being processed.
Advantageously, the format calculator automatically converts servo frame numbers to the associated sector number on track on-the-fly. This reduces processor bandwidth consumption and also supports zero latency read/write operations in hard drive systems. Other aspects and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.